The present invention is directed to a viscous fluid coupling for a motor vehicle, more particularly to a viscous fluid coupling for controlling the rotation of an engine cooling fan in response to changes in temperature of the engine cooling water.
In conventional viscous fluid couplings of this type, when the vehicle engine is shut off, a substantial amount of viscous fluid remains within the fluid operating chamber. Therefore, upon starting the cold engine the viscous fluid remaining within the operating chamber will cause the fan to rotate at a substantial speed thereby unduly prolonging the warmup period for the engine. Furthermore, in conventional viscous fluid couplings, the communication between the fluid reservoir chamber and the fluid operating chamber is generally controlled by means of a swinging valve plate making it very difficult to obtain a good seal between the valve plate and the communication passage between the fluid reservoir and the fluid operating chamber.